M07: Q25

Think in this way..
assume 100 sucide attemps..
25 successful 75 unsuccessfull.
40% of unsuccessful suicide attempts are repeated =40% sucide attempts are second attempt = 30

% first atttempt = 100-30 =70%

I don't agree with this method, since it assumes that out of the 25 successful attempts, none of them were re-attempts. It only considers the 75% unsuccessful, but for all we know, from the 25 successful attempts, a good portion of them may have been repeats.

I agree with the OA and kept getting 77%.

100 people = 100 attempts
25 successful, 75 not
75 not, 40% repeat = 35 repeats
35 repeats, 25% success = 7.5 success

so out of the total suicides, 32.5, 25 were first attempts or 77%.

Even if we lengthen the time,
100 people = 100 attempts
25 successful, 75 not
75 not, 40% repeat = 35 repeats
35 repeats, 25% success = 7.5 success, 27.5 not
27.5 not, 40% repeat = 11 repeats
11 repeats, 25% success = 2.75 successful

so out of the total suicides, 25+7.5+2.75 = 32.5, 32 were first attempts 77% were first attempts, i don't think it would ever converge to 70%.

so why isn't the answer 77

Attempts = 100
Successful = 25
Un-successful = 75
Repeat = 40% of unsucessful = .4x75 = 30

New attempt = 100 - 30 = 70

Probably any is not correct here. Any includes the first month in which all (100%) sucides are first attempt.

There is no initial month on this problem. Given that it asks for percentages, the word "any" is not relevant, as the percentage will be the same for any period.

The question does not ask "what percentage of attempted suicides in any 6 months period is a first attempt?".

It asks "what percentage of suicides in any 6 months period is a first attempt?".

Therefore, the official explanation is wrong.

Attempts = 100
Successful = 25
Un-successful = 75
Repeat = 40% of unsuccessful = .4x75 = 30
Succesful repeats = 25% of 30 = 7.5

1st attempt successful / total suicides = 1st attempt successful / (1st attemp successful + 2nd attempt successful) = 25 / (25 + 7.5) = 77%

This question should be revised.

Cheers

It should be 77 as explained above.
This question really needs revision.

I have some trouble understanding the solution. Please see my reasoning below and advice.

Assume that in each 6 month period the first time attempts are 100.
In the first attempt -
Attempt - 100
Successful - 25
Unsuccessful - 75

In the second attempt -
Attempt = 100 + 30 (40% of Unsuccessful from previous attemp) = 130
Successful - 32.5
Unsuccessful - 97.5

First time attempts as a percentage = (130-30)/130 * 100 = 77%

The OA assumes that 100 attempts in the second attempt include re attempts as well. Is it right?

reminder from latest test taker, please revise the answer to 77% :-D